The present invention relates to a process for cooling gases that contain particles which tend to form cake-like deposits during the cooling process. The process involves heat exchange with a vaporizing coolant and an intermediate carrier that is contained in annular chambers between the gases and the cooling medium. The annular chambers are formed by double-walled tubes which are arranged within a chamber that contains the cooling medium. The present invention relates further to a heat exchanger, in particular a heat exchanger that is used for such a process.
The gases of the kind described above deposit their component parts, which either liquify or solidify during the cooling process, on the cooling surfaces. The deposits become heavier when the temperature of the cooling surfaces relative to the temperature of the gases becomes lower. If cooling is effected in tubes that are surrounded by a circulating cooling medium that vaporizes around the tubes, the gas-side surface temperature of the tube will be close to the vaporization temperature of the cooling medium, i.e., it will be relatively low. The resulting deposits of the separated components of the gases will thus be heavy, even after a brief period of operation, and will cause considerable deterioration of thermal transfer. They will also cause an elevated pressure loss of the gas.
German Pat. DE-PS No. 29 33 748 describes a heat exchanger in which a process of this sort can be carried out. In this heat exchanger, the disadvantages outlined above have been avoided by the use of a cold so-called tempering gas that is free of additives. The gas is introduced into an annular chamber formed by gas transfer tubes and cooling agent tubes, and is then mixed with the gas that is to be cooled by means of vortexing. This heat exchanger requires the availability of a specially cooled, additive-free tempering gas. In addition from the operational point of view, it is difficult to arrive at and control the correct mixture of gas and tempering gas. The heat exchanger entails higher construction costs and because of its design, the quantity of tempering gas increases with the quantity of gas.
German laid-open patent application DE-OS No. 31 36 860 describes a heat exchanger used to cool hot gases containing components that are deposited during the cooling process. This heat exchanger has double-walled tubes and cooling-medium chambers formed between two tube bases. Water is passed between the annular chambers of the double-walled tubes so that--as a result of the predominant surface temperature--deposits of coke, for example, form on the inner wall of the tubes that carry the gas. From time to time these deposits are removed either mechanically or are burned off. The double-walled tubes are arranged within an open casing that contains no cooling agent.